Is a polytunnel better than a greenhouse?

They do different things well, and the choice comes down to what you are growing and how much you mind how it looks — the price difference is real but smaller over time than it first appears.

Greenhouse — glass or rigid polycarbonate on a frame.

Better light transmission, and it stays good for decades with glass.

Retains heat better overnight, particularly with glass and a solid base, so the frost-free season is slightly longer.

Long-lived. A glass greenhouse can last 30 years or more.

Easier to heat and to seal, and better suited to overwintering tender plants and to propagation with a heated bench.

Looks like a permanent structure, which matters in a small or ornamental garden.

Costs considerably more to buy and to install, and needs a level base.

Polytunnel — polythene sheeting stretched over steel hoops.

Far more growing space for the money — several times the area for a comparable outlay.

Better for growing in the ground, which suits crops directly: tomatoes, cucumbers, beans, salad, and extending the season on brassicas.

Diffuse light, since polythene scatters it. This is genuinely an advantage for even growth and reduces scorch.

The cover degrades. Polythene typically needs replacing every five to ten years depending on grade, which is the main ongoing cost.

Ventilation is harder. Doors at both ends is usually the only option, and tunnels overheat readily in summer — this is the most common complaint and it needs planning for.

More vulnerable to wind damage, and a tear spreads. Siting and anchoring matter enormously.

Condensation drips, and humidity encourages fungal disease without good airflow.

The practical summary: for volume vegetable growing, a polytunnel gives far more for the money. For propagation, overwintering, tender ornamentals and small gardens, a greenhouse is better. Many allotment growers eventually have both, and a cold frame covers a surprising amount of the same ground for very little.

Check whether planning permission applies for a large structure near a boundary.